Cool questions but you're taking the fun out of bleach!
I think the souls just have longer life spans than humans. Because they still age and are still affected by sickness. And aging is a process of death so yeah, i think they just live much much longer.
If souls die, i think its safe to assume that in the bleach universe, they just cease to exist. Saying that there is a hell and heaven ON TOP soul society and the hollow place is just too much for me, lol
I dont think souls get reincarnated naturally. (probably through some plot twist type of thing...)
And ive read somewhere that souls have the choice to be born again in the living world (i think this is the reincarnation thing you were talking about). What im slightly confused about is if they retain memories, spirit level, or appearance. There's probably some process they have to go through in order to do it. I'm not too sure but I remember in the anime/manga when they explained why the shinigami and the quincies don't get along is cuz the Quincies destroy them while the Shinigami purify them and that the Quincies disrupt the ratio of souls entering Soul Society and souls entering the Human World.
What i can't help thinking is that with clans that share blood (like clans from Naruto and the Quincy)...how the hell do they have pure clan members that aren't retarded! I mean COME ON!
Aizen is gangsta for making everyone wear white.
Tousen: "So what are we going to wear anyway? how do we tell each other apart from the shinigami?"
Aizen: "I GOT IT....lets wear exactly what they wear...but make it WHITE!"
Ichimaru: "OH SH*T, now THATS gangsta!"
Tousen: "....even I wouldn't say that..."
Aizen: "Loosen up Tousen...check this out...lets show him Gin!"
Tousen: "... 0_0 ..."